1. Field of the invention
The invention generally relates to optical drives and laser power control methods, and more particularly to a system and a method for Constant Angular Velocity control format.
2. Description of the Related Art
Among optical recording drives, control format for recording can be categorized into CAV (Constant Angular Velocity) and CLV (Constant linear Velocity) control formats. With CAV control format, a disk rotates at a constant speed regardless of what area of the disk is being accessed. Rotational speed of a spindle in the optical recording drive is constant. Data are recorded into tracks of an optical disk. Tracks are formed in a spiral line extending from the inner to the outer of an optical disk. On the other hand, the purpose of CLV is to ensure a constant data rate regardless of where on the disk the data is being accessed. With CLV, the rotation speed of the disk changes based on how close to the center of the disk the data is. For tracks near the center, the disk rotates faster, and for data on the outside, the disk rotates slower.
Current CD-ROM or CD-RW drive uses CLV control format for disk recording. Data is recorded at a uniform density with CLV control format onto a disk. As the high rotational speed of the spindle develops, CLV control format cannot cope with the demands come with high rotational speed. A recent development utilizing a CAV control format recording, whereas disk data recording performance approximates to the resulted uniform density from CLV control format recording. For example, for an optical drive under 16 times CLV control format, the rotational speed of inner tracks is 800 rpm. In contrast, for an optical drive using 16 times CAV control format recording, performance of the outer tracks recording can be as high as the performance gained from an optical drive using 40 times CLV control format recording.
In order to cope with the spindle operation adapting a CAV control format, two technical problem must be resolved: one is laser power has to be subject to the linear velocity changes, the other is recording pulse has to be subject to the linear velocity changes of a disk.